CVE-2024-35202 in Bitcoin
Summary
by MITRE • 10/10/2024
Bitcoin Core before 25.0 allows remote attackers to cause a denial of service (blocktxn message-handling assertion and node exit) by including transactions in a blocktxn message that are not committed to in a block's merkle root. FillBlock can be called twice for one PartiallyDownloadedBlock instance.
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Analysis
by VulDB Data Team • 10/15/2024
This vulnerability exists in Bitcoin Core versions prior to 25.0 and represents a critical denial of service flaw that can be exploited by remote attackers to disrupt network operations. The vulnerability specifically targets the blocktxn message handling mechanism within the Bitcoin protocol implementation, where malicious actors can craft specially constructed blocktxn messages that contain transactions not properly committed to in a block's merkle root. This creates a fundamental inconsistency in the blockchain validation process that the software cannot properly handle, leading to assertion failures and subsequent node termination.
The technical flaw stems from an improper handling of the PartiallyDownloadedBlock instance within the FillBlock function, which can be invoked twice for the same instance during the block processing cycle. This double invocation creates a scenario where the software attempts to process transactions that do not align with the merkle root commitment, causing an assertion failure that terminates the node. The vulnerability is particularly dangerous because it operates at the network level where nodes communicate and validate blocks, making it an attractive target for attackers seeking to disrupt the Bitcoin network's operation. This flaw directly relates to CWE-611 Improper Restriction of XML External Entity Reference and CWE-129 Improper Validation, as it involves inadequate validation of transaction data and improper handling of external inputs.
The operational impact of this vulnerability extends beyond individual node failures to potentially compromise the overall health and stability of the Bitcoin network. When multiple nodes are affected simultaneously, it can lead to reduced network participation, slower block propagation, and increased orphaned blocks that disrupt the consensus mechanism. Attackers can exploit this vulnerability by sending malicious blocktxn messages to targeted nodes, causing them to crash and exit the network, thereby reducing the network's redundancy and resilience. The vulnerability also has implications for the broader Bitcoin ecosystem as it can be used to perform network-level disruption attacks that may affect mining operations, wallet services, and other network participants. This aligns with ATT&CK technique T1499.004 Network Denial of Service, where adversaries leverage software vulnerabilities to disrupt network availability.
Mitigation strategies for this vulnerability require immediate deployment of Bitcoin Core version 25.0 or later, which contains the necessary patches to prevent the double invocation of FillBlock and properly validate transaction commitments against merkle roots. Network operators should also implement additional monitoring and alerting systems to detect unusual node behavior patterns that may indicate exploitation attempts. The patch addresses the core issue by ensuring proper validation of PartiallyDownloadedBlock instances and preventing the duplicate function calls that lead to assertion failures. Organizations should also consider implementing rate limiting and transaction validation checks at the network level to reduce the impact of potential exploitation attempts. Regular security audits and updates remain essential to protect against similar vulnerabilities that may arise in complex distributed systems like Bitcoin.